The present invention relates to a chemical adsorbent which can form a monomolecular thin film wherein component molecules are aligned in a predetermined direction, a liquid crystal alignment layer utilizing the same and a liquid crystal display device utilizing the same, and additionally, a method of manufacturing the above-mentioned chemical adsorbent and the like.
In recent years, although a liquid crystal display device has been spread rapidly as a means of actualizing the downsizing and lightening of information apparatus, coating materials for manufacturing a liquid crystal alignment layer, which is an important constituent of the device, are limited. Consequently, a new material for the alignment layer having an unprecedented characteristic is desired according to the improvement of a liquid crystal display device in performance.
A color liquid crystal display device has a structure wherein a pair of substrates with a transparent electrode arrayed generally in a matrix and a liquid crystal alignment layer formed on the transparent electrode are opposed through the liquid crystal alignment layers with a certain gap and a liquid crystal is sealed between the gap. More specifically, a macromolecular film is formed on each surface of a first glass substrate with a pixel electrode and a thin-film transistor (TFT) array and a second glass substrate with a plurality of red, blue and green color filters and a common transparent electrode on the color filters, and an alignment of the liquid crystal is provided by rubbing the coated planes. Secondly, the first glass substrate and the second glass substrate are opposed through the coated planes (the liquid crystal alignment layers) with a spacer interposed, and an empty cell (a panel structure) is made by adhesion of a periphery of the substrates. A liquid crystal display device is constituted by sealing with an injection of such a liquid crystal as twisted nematic (TN) into the empty cell, and additionally, a liquid crystal display device as a optical display device is constituted by disposing polarizers on the front and back sides of the device as well as a backlight outside the first glass substrate.
A liquid crystal display device having such a structure applies a voltage between the electrodes to obtain an ON/OFF state with the TFT and controls a light transmission by changing an alignment state of the liquid crystal and displays an arbitrary image. Therefore, the liquid crystal alignment layers for controlling the alignment state of the liquid crystal on a path of the light transmission play an extremely important role of affecting a display performance.
A polyimide film has conventionally been used widely as coating materials for such a liquid crystal alignment layer in terms of superiority in affinity with the liquid crystal, heat-resistance and adhesion to the substrate. The following methods are used for manufacturing the polyimide film: a method wherein the polyimide film is made by changing the polyamic acid into imide while burning the substrate after rotational-coating on a substrate a solution wherein polyamic acid, which is a precursor polymer of polyimide, is dissolved in such an organic solvent as xylene; and a method wherein the polyimide film is made by evaporating the solvent after rotational-coating on a substrate a solution wherein polyimide is dissolved in such organic solvents as DMF (N,N-dimethylformamide), DMAc (dimethylacetamide), butylcellosolveacetate and N-methyl-2-pyrrolidone.
However, a polyimide film has the following problems and thereby is not enough satisfactory for a liquid crystal alignment layer. That is:
(1) In the method by using polyamic acid which is a precursor substance, it is necessary to burn at a high temperature of 250xc2x0 C. and above in order to change into imide sufficiently. In the method by using polyimide, it is necessary to remove the solvent at a considerably higher temperature because of no low boiler suitable for dissolving the polyimide. Such organic solvents as the above-mentioned DMF, DMAc, butylcellosolveacetate and N-methyl-2-pyrrolidone can be used as a solvent for dissolving the polyimide. however, since every solvent has a high boiling point (153xc2x0 C., 165xc2x0 C., 192xc2x0 C., 202xc2x0 C. respectively) and is flammable, it is necessary to consider explosion-protection while manufacturing the polyimide film by evaporating and drying the solvent at a high temperature. Consequently, a particular device is necessary for heating in manufacturing a polyimide film, whereby its manufacturing costs are raised. Moreover, there is the possibility that such a circuit as TFT will be damaged by heating.
(2) Furthermore, since polyimide is not sufficiently made into a film, it is difficult to manufacture a thin film with a uniform coating thickness. Consequently, since display unevenness resulting from non-uniformity of coating thickness occurs and a thick film functions as an insulation film, another problem is that it is difficult to actualize a liquid crystal display device having a low driving voltage.
(3) In addition to the above, the following problems are caused in rubbing operation for providing an alignment.
1 If a film has irregularities on its surface, recessed portions fail to be rubbed, particularly, in the case of a panel with a large area, the panel fail to be rubbed uniformly. Accordingly, such problems are caused as the occurrence of alignment defect and display unevenness, and display sticking.
2 Furthermore, static electricity is generated on an alignment layer and the static electricity results in deteriorating the function of a TFT.
3 In addition, dust comes out of rubbing materials (cotton cloth or the like) and the dust results in display unevenness and a change of a substrate gap.
Consequently, various noncontact type aligning methods are proposed for the purpose of solving the above-mentioned problems in a rubbing method.
In Japanese Unexamined Patent Publication No. 5-53118, a technique is proposed wherein a layer of a photosensitive composition is formed on a substrate, grooves of a predetermined pattern are formed on the composition layer by exposing and heat-treating, and an alignment is provided by the grooves. However, the technique requires high photo energy for forming the grooves. Moreover, since it is difficult to form uniform grooves, such problems are caused as the occurrence of display unevenness and the like, and alignment control force is not sufficient.
In Japanese Unexamined Patent Publication No. 7-72483, a technique is proposed wherein an alignment is provided by polymerizing the polyimide or the like while irradiating linearly polarized light to a compound layer for forming an alignment layer comprising polyimide or polyimide precursor. However, since the technique uses polyimide which is an organic polymer, the technique can not solve a problem of a rise in a liquid crystal driving voltage caused by a thick coating. Another problem is that the fixing force of an alignment layer on a substrate is not sufficient.
In Japanese Unexamined Patent Publication No. 7-318942, a technique is proposed wherein a molecular structure having an alignment is made by causing another reaction of combination or decomposition in a molecular chain of the alignment layer while irradiating from a diagonal direction to an alignment layer having a macromolecular structure. However, since the technique also is intended for an alignment layer which is made of such organic polymers as polyimide, polyvinyl alcohol and polystyrene, the technique can not solve the above-mentioned problems of a thick coating and a low fixing force on a substrate. Moreover, the irradiation from a diagonal direction to an alignment layer is essential for providing a pretilt angle and the technique requires a irradiation device with high precision for irradiating accurately from a diagonal direction, whereby manufacturing costs are raised.
In addition to the above-mentioned problems, the problem of a liquid crystal display device in a twisted nematic mode or the like is that a viewing angle is narrower than in the past. As a method for solving the problem, in Japanese Unexamined Patent Publication No. 5-173135, a method is proposed wherein a plurality of areas having different alignment directions of a liquid crystal are formed by repeating rubbing in a reverse direction after rubbing an alignment layer in a certain direction and covering the portions concerned with a resist.
Yet, in the rubbing (contact type) method, a troublesome operation of rubbing while masking each divided section must be repeated for forming a plurality of sections having different alignment directions of a liquid crystal. Consequently, according to this technique, even more serious problem is that the manufacturing efficiency of an alignment layer deteriorates largely as well as dust comes out.
On the other hand, a plurality of areas having different alignment directions of a liquid crystal can be formed also by applying each of such above-mentioned techniques as Japanese Unexamined Patent Publication No. 5-53118 and the like. However, as described above, since each of the above-mentioned techniques has such problems as a thick coating and an insufficient fixing force on a substrate, nevertheless a liquid crystal alignment layer, which is enough satisfactory, can not be provided by utilizing these techniques.
The inventors of the present invention, in Japanese Unexamined Patent Publication No. 3-7913, proposed a technique wherein an alignment layer with a coating thickness in nanometer order can be manufactured with a high productivity. The technique uses as an alignment layer a monomolecular film which is made by chemisorbing a silane-based chemical adsorbent (or called surface active agent) on a substrate plane. According to the technique, an extremely thin and transparent film in a state combined and fixed on a substrate can be formed easily and efficiently, and additionally, an alignment layer having a certain alignment control force over liquid crystal molecules can be provided without rubbing. However, the technique still leaves room for improving on the thermal stability of alignment, the strength of alignment control force and the like.
The present invention has been intended in response to the above-mentioned problems. A series of the present invention described below seeks to solve the above-mentioned problems at one effort. The purposes of a series of the present invention are: first, to provide a new chemical adsorbent which can form an extremely thin and transparent film in nanometer order which is fixed uniformly and firmly on a substrate, and give an alignment characteristic of high thermal stability to the thin film; secondly, to provide a liquid crystal alignment layer having a desirable alignment characteristic, a superior alignment control force over liquid crystal molecules, and a superior thermal stability by using the above-mentioned chemical adsorbent; thirdly, to provide a liquid crystal display device which is superior in a display performance by using the above-mentioned liquid crystal alignment layer; lastly, to provide a method of manufacturing each of the above-mentioned chemical adsorbent, liquid crystal alignment layer and liquid crystal display device with a high productivity.
Although a series of the present invention has been intended through a series of research and development which is closely relevant, each of a series of the present invention is described in different embodiments. Therefore, after a series of the present invention is divided into the first to sixth invention group, each group will be detailed below.
A chemical adsorbent in the first invention group is characterized by the following constitution.
(1) A chemical adsorbent consisting of a compound comprising a group of CR1CR2CO and a functional group having Si in its chemical structure.
According to a compound having the above-mentioned composition, the functional group having Si functions as a chemisorbed group. Therefore, the compound can be chemically bonded (chemisorbed) through the functional group having Si on a substrate plane having such hydrophilic groups as OH group, COOH group, NH2 group, NH group and SH group. Moreover, a vinyl group functions as a photoreactive group. Therefore, molecules can be crosslinked to each other through the vinyl group by irradiating.
A significance of using a chemical adsorbent having the above-mentioned composition as a material for a liquid crystal alignment layer is as follows. A thin film, which is formed by contacting the above-mentioned chemical adsorbent on a substrate and chemisorbing it, has a monolayer-like structure wherein a molecule, in which an end (a functional group having Si) in a direction of its major axis is bonded on the substrate plane and the other end is aligned in a direction opposite to the substrate, is arrayed in a lateral direction. The film is an extremely thin film in nanometer order, and transparent in a range of visible ray and chemically stable. Meanwhile, the film has a characteristic in which a photoreaction is caused in a vinyl group by irradiating a light in a range of ultraviolet rays. Therefore, after chemisorbing the above-mentioned chemical adsorbent on a substrate, it is possible to crosslink and connect component molecules to each other by irradiating ultraviolet rays, and thereby stabilize an alignment of the component molecules in a steric structure. In addition, if a polarized light is used in irradiating ultraviolet rays, it is possible to cause a crosslinking along a certain direction and thereby control an alignment direction of the component molecules by determining a polarized direction.
In a thin film wherein adsorbent molecules are arrayed in parallel with a substrate plane, a liquid crystal molecule can enter each gap (valley) between component molecules. Therefore, a thin film wherein the component molecules are aligned in a certain direction has a particular alignment of a liquid crystal. Moreover, since each of the component molecules is involved in an alignment of a liquid crystal, the above-mentioned thin film indicates a strong alignment control force despite an extremely thin film. Furthermore, since a component molecule is connected to each other by crosslinking, an alignment is not deteriorated by an external stimulus such as heat and rubbing. In addition, since the film is extremely thin and transparent, and not an organic polymer film, it scarcely functions as an electrical resistance film. Therefore, the film has an extremely appropriate characteristic for a liquid crystal alignment layer, in which a light transmission and an electric field for driving a liquid crystal are not hindered.
Meanwhile, a conventional liquid crystal alignment layer (such as a polymer film made of the above-mentioned polyimide), which is composed closely in a state wherein a long main chain is tangled up, has difficulty in obtaining a sufficient alignment control force since only a surface of the film can contribute to an alignment of a liquid crystal. Moreover, in a conventional alignment layer for which an alignment is provided by rubbing, the alignment is changed or deteriorated by an external stimulus such as heat and rubbing. Furthermore, since such a polymer film as polyimide has a thick coating and a high electrical resistance, it is a hindrance factor to a light transmission and a liquid crystal driving.
In a chemical adsorbent having a chemical structure in which component molecules can not be crosslinked to each other, a monomolecular thin film can be formed; however, a stable alignment characteristic can not be obtained. For instance, since a chemical adsorbent, which is written in the above-mentioned Japanese Unexamined Patent Publication No. 3-7913, does not have a photoreactive group, adsorbent molecules can not be chemically connected to each other. Therefore, the problem is that an alignment is deteriorated by the heat of around 200.
A chemical adsorbent having the above-mentioned composition is extremely useful as a material for a liquid crystal alignment layer, and a use for the adsorbent is not limited to this. A use for a chemical adsorbent in other invention groups is not limited, either.
In the above-mentioned composition, it is preferable to add the components described below in (2) to (4). According to a composition to which the following components are added, an effect of the above-mentioned function can be actualized even more certainly. That is:
(2) In the above-mentioned composition, it is possible to make a functional group having Si a compound which is bonded to an end of CO in a group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94. Each of R1 and R2 is a hydrogen, an alkyl group having 1 to 3 C or an alkoxy group having 1 to 3 C.
The groups of xe2x80x94CH3, xe2x80x94C2H5 and xe2x80x94C3H7 can be cited as the above-mentioned alkyl group having 1 to 3 C, and the groups of xe2x80x94OCH3, xe2x80x94OC2H5 and xe2x80x94OC3H7 can be cited as the above-mentioned alkoxy group having 1 to 3 C.
(3) It is possible to make the compound in the above-mentioned (2) a compound represented by the following Chemical Formula 1. In Chemical Formula 1, n is an integer of 1 to 14 inclusive, R is an alkyl group having 1 to 14 C or a phenyl group, X is a halogen, an alkoxyl group or an isocyanato group, m is an integer of 1 to 3 inclusive and A is a functional group. 
(4) It is possible to make the compound in the above-mentioned (2) a compound represented by the following Chemical Formula 2, Chemical Formula 3 or Chemical Formula 4. In the following Chemical Formulae 2 to 4, n is an integer of 1 to 14 inclusive, R is an alkyl group having 1 to 14 C or a phenyl group, X is a halogen, an alkoxyl group or an isocyanato group, m is an integer of 1 to 3 inclusive (an integer of 1, 2 only in Chemical Formula 4) and A is a functional group. 
A liquid crystal alignment layer in the first invention group, which is formed by using the above-mentioned chemical adsorbent, is characterized by the following constitution.
(5) A liquid crystal alignment layer wherein liquid crystal molecules can be aligned in a particular direction, a chemical adsorbent comprising a group of xe2x80x94CR1xe2x80x94CR2xe2x80x94COxe2x80x94 and a functional group having Si in its chemical structure is bonded and fixed directly or with an interposition of a different substance layer on a substrate surface through Si, and an adjacent component molecule is crosslinked to each other through at least one bond of a double bond of Cxe2x95x90C in the group of xe2x80x94CR1xe2x80x94CR2xe2x80x94COxe2x80x94.
(6) A liquid crystal alignment layer wherein liquid crystal molecules can be aligned in a particular direction, consisting of a compound comprising a chemical bond unit represented by the following Chemical Formula 5, Chemical Formula 6, Chemical Formula 7 or Chemical Formula 8. In the following Chemical Formulae 5 to 8, n is an integer of 1 to 14 inclusive and R is an alkyl group having 1 to 14 C or a phenyl group.
Since this composition comprises a chemical bond unit represented by the following Chemical Formulae 5 to 8, an alignment function on liquid crystal molecules is large, and particularly, a function of aligning a twisted nematic (TN) type liquid crystal is large. Therefore, a liquid crystal alignment layer having this composition can be used appropriately as a liquid crystal alignment layer for a liquid crystal display device in a TN mode. 
The following constitutions can be adopted as a method of manufacturing a liquid crystal alignment layer having the above-mentioned composition.
(7) A method of manufacturing a liquid crystal alignment layer comprising the steps of producing a chemisorption solution by dissolving a silane-based chemical adsorbent comprising a group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94 and a functional group having Si in a nonaqueous solvent; forming a monomolecular thin film which is made of the above-mentioned silane-based chemical adsorbent on a substrate plane by contacting the above-mentioned silane-based chemisorption solution on the substrate plane, and chemisorbing it on the substrate plane; and photopolymerizing adsorbent molecules to each other at a double bond of Cxe2x95x90C in the group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94 by irradiating an ultraviolet ray or a far-ultraviolet ray on the above-mentioned thin film plane.
(8) In the above-mentioned composition, it is possible, between the above-mentioned steps of forming a thin film and photopolymerizing, to provide a step of treating a provisional alignment of molecules composing the thin film by drain-drying an organic solvent in a certain direction after contacting the above-mentioned organic solvent on the thin film plane.
According to this composition, an alignment of a liquid crystal can be provided to some extent.
(9) It is possible, between the above-mentioned steps of forming a thin film and photopolymerizing, to provide the steps of washing the thin film plane with a nonaqueous solvent to remove the chemical adsorbent which is not yet adsorbed; and aligning provisionally an alignment direction of molecules of the silane-based chemical adsorbent which is chemisorbed on the substrate plane by drain-drying the nonaqueous solvent remaining on the substrate plane while setting up the substrate through washing in a certain direction.
According to this composition, a liquid crystal alignment layer, which is made of a monomolecular thin film with a more stable alignment function, can be provided.
(10) It is possible to execute an irradiation of the ultraviolet ray or the far-ultraviolet ray in the above-mentioned step of photopolymerizing through a polarizer, a transparent plate having a multitude of grooves of 0.1 to 0.3 xcexcm in width on its surface or a transparent plate on which rubbing is executed.
According to this composition, a direction of photopolymerizing can be controlled in a polarized direction, a groove direction or a rubbing direction.
(11) It is possible to execute an irradiation of the ultraviolet ray or the far-ultraviolet ray in the above-mentioned step of photopolymerizing through a patterned mask which is put further on a polarizer, a transparent plate having a multitude of grooves of 0.1 to 0.3 xcexcm in width on its surface or a transparent plate on which rubbing is executed, and thereby control a direction of a chemical bond between chemisorbed molecules and change an alignment direction of adsorbent molecules in each patterned irradiation area.
In this composition, a liquid crystal alignment layer in a multidomain alignment, wherein a plurality of small sections into which a pixel is divided differ from each other in a liquid crystal alignment direction, can be manufactured by executing a light irradiation more than once, such as changing a polarized direction.
(12) In the above-mentioned step of producing a chemisorption solution, it is possible to use a multicomponent chemisorption solution wherein a first silane-based chemical adsorbent and a second silane-based chemical adsorbent, which differs from the first silane-based chemical adsorbent in a molecular length, are mixed at a predetermined ratio.
According to this composition, a degree of photopolymerization of the first silane-based chemical adsorbent and/or the second silane-based chemical adsorbent can be changed by changing a mixture ratio. Moreover, an inclination of longer adsorbent molecules to a substrate can be controlled with shorter adsorbent molecules by determining a mixture ratio properly. Furthermore, since it is possible to change a density of a polymerizable group, a degree of photopolymerization can be controlled.
(13) In the above-mentioned (12), it is possible, between the above-mentioned steps of forming a thin film and photopolymerizing, to provide a step of treating a provisional alignment of molecules composing the thin film by drain-drying a nonaqueous solvent in a certain direction after contacting the above-mentioned nonaqueous solvent on the thin film plane.
According to this composition in which a light is irradiated after aligning an adsorbent molecule provisionally, a particular alignment characteristic of a liquid crystal can be provided even more certainly.
(14) In the above-mentioned (12), it is possible, between the above-mentioned steps of forming a thin film and photopolymerizing, to provide the steps of washing the thin film plane with a nonaqueous solvent to remove the chemical adsorbent which is not yet adsorbed; and aligning provisionally an alignment direction of molecules of the silane-based chemical adsorbent which is chemisorbed on the substrate plane by drain-drying the nonaqueous solvent remaining on the substrate plane while setting up the substrate through washing in a certain direction.
According to this composition, through a series of operations of washing and drying, the chemical adsorbent which is not yet adsorbed can be removed as well as the adsorbent molecules can be aligned provisionally.
(15) In the above-mentioned (12), it is possible to execute an irradiation of the ultraviolet ray or the far-ultraviolet ray in the above-mentioned step of photopolymerizing through a polarizer, a transparent plate having a multitude of grooves of 0.1 to 0.3 xcexcm in width on its surface or a transparent plate on which rubbing is executed.
(16) In the above-mentioned (12), it is possible to execute an irradiation of the ultraviolet ray or the far-ultraviolet ray in the above-mentioned step of photopolymerizing through a patterned mask which is put further on a polarizer, a transparent plate having a multitude of grooves of 0.1 to 0.3 xcexcm in width on its surface or a transparent plate on which rubbing is executed, and thereby control a direction of a chemical bond between chemisorbed molecules and change an alignment direction of adsorbent molecules in each patterned irradiation area.
A liquid crystal display device in the first invention group, which is formed by using a liquid crystal alignment layer having the above-mentioned composition, can be composed as described below.
(17) A liquid crystal display device comprising, at least, two opposite substrates with an electrode on an inside plane, a liquid crystal alignment layer which is formed on an inside plane of at least one of the above-mentioned opposite substrates, and a liquid crystal which is received into a gap between the above-mentioned opposite substrates, wherein the above-mentioned liquid crystal alignment layer is a monomolecular thin film which is formed by chemisorbing a chemical adsorbent directly or through a different substance layer on the above-mentioned substrate plane, and adsorbent molecules are crosslinked to each other along a particular direction.
Since a rubbingless liquid crystal alignment layer, which is low in a deterioration of an alignment, is used in this composition, a liquid crystal display device with a high reliability can be provided.
(17-1) A liquid crystal display device of an in-plane switching (IPS) type in which an electrode and an opposite electrode are formed on the same substrate, wherein the above-mentioned liquid crystal alignment layer is a monomolecular thin film which is formed by chemisorbing a chemical adsorbent directly or through a different substance layer on the above-mentioned substrate plane, and adsorbent molecules are crosslinked to each other along a particular direction.
Since a rubbingless liquid crystal alignment layer, which is low in a deterioration of an alignment, is used in this composition, a liquid crystal display device in an in-plane switching (IPS) mode can be provided with a high productivity.
(18) In the above-mentioned (17) and (17-1), the chemical adsorbent comprises a group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94 and a functional group having Si, and the above-mentioned adsorbent molecules are crosslinked to each other at a double bond of Cxe2x95x90C in the group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94.
(19) In the above-mentioned (18), the thin film has a different liquid crystal alignment control direction at each of a plurality of small patterned sections into which a pixel unit is divided.
The following constitutions can be adopted as a method of manufacturing a liquid crystal display device having the above-mentioned composition.
(20) A method of manufacturing a liquid crystal display device comprising the steps of producing a chemisorption solution by dissolving a silane-based chemical adsorbent comprising a carbon chain as well as a group of xe2x80x94CR1xe2x95x90CR2xe2x80x94COxe2x80x94 and a functional group having Si at an end of or inside the above-mentioned carbon chain in a nonaqueous solvent; forming a monomolecular thin film by contacting the above-mentioned chemisorption solution on a first substrate with at least a group of electrodes in a matrix, and chemisorbing the chemical adsorbent on the above-mentioned substrate plane at the functional group having Si; aligning adsorbent molecules provisionally by drain-drying the nonaqueous solvent for washing while setting up the above-mentioned substrate in a certain direction after washing the above-mentioned thin film with a nonaqueous solvent; providing an alignment characteristic by means of producing the first substrate with a liquid crystal alignment layer having a particular alignment characteristic by irradiating an ultraviolet ray or a far-ultraviolet ray on the provisionally aligned thin film, and crosslinking the adsorbent molecules to each other in a particular direction through a photopolymerization; producing an empty cell by sticking and fixing a periphery of the substrates after joining through the electrode plane with a predetermined gap the above-mentioned first substrate with a liquid crystal alignment layer as well as an opposite substrate or a second substrate with a liquid crystal alignment layer having an opposite electrode, which is produced like the above-mentioned first substrate with a liquid crystal alignment layer; and injecting a liquid crystal into the above-mentioned empty cell.
(21) It is possible to adopt a method of exposing through a patterned mask which is put on a polarizer in irradiating the ultraviolet ray or the far-ultraviolet ray in the above-mentioned step of providing an alignment characteristic.
According to this method, a controlled direction of a liquid crystal alignment can be changed at each of a plurality of small patterned sections into which a pixel unit is divided by controlling a crosslinking direction of the adsorbent molecules.